This invention relates to a photochemical reaction process and apparatus therefor.
High pressure mercury lamps and low pressure mercury lamps are known ultraviolet light sources which have been employed in the semiconductor manufacture field. Such a mercury lamp is capable of emitting ultraviolet rays by virtue of argon gas excited by an alternating electric power of the line frequency (50 Hz), the argon gas being disposed in the lamp at a pressure of several Torrs with a dopant gas of mercury.
FIG. 1 shows the relative energy level versus the frequency of ultraviolet rays emitted from an conventional mercury lamp. As shown in the diagram, the energy level is highest at 253.7 nm and the next high at 184.9 nm. However, the most useful ultraviolet rays in semiconductor manufacture are those having a wavelength of 184.9 nm which is effective to decompose silane (Si.sub.n H.sub.2n+2, n is a positive integer). For this reason, it is desired to enhance the emission at about 185 nm.
Further, in accordance with a conventional photo-CVD, ultraviolet rays are emitted through a glass window to irradiate a reactive gas together with a substrate to be processed so that the product of the CVD is deposited also on the inside surface of the window besides the substrate and reduces the transmission of the rays to the inside of the reaction chamber resulting in the deposition being stopped.
Still further, the emission from conventional lamps is necessarily intermittent as shown in FIGS. 2(A) and 2(B) and therefore the film eventually formed becomes non-uniform. In the figures are schematically illustrated the curves showing the applied current C and the corresponding applied voltage V.